Biosynthesis of hcG subunits in choriocarcinoma cells has been studied by incorporation of labeled carbohydrate precursors combined with gel filtration of glycopeptides obtained by pronase digestion of immunoprecipitated subunits before and after exoglycosidase treatmenmt. The large molecular weight free hCG-Alpha contained more labeled fucose and sialic acid than the smaller combined Alpha. Inhibition of glycosylation with tunicamcin impaired subunit combination but not secretion.